when napa creek overflowed its banks. this time it didn't. thanks mostly to 35 million dollar federally funded bipass project by the army corps of engineers. >> design worked as intended. >>reporter: project simple and condition september more difficult next cushion. really a matter of rechanneling water. below my feet this culvert has doubled x's ty. if it weren't here last weekend the area probably would have flooded. >> it can be dramatic. very fast. and it can create significant damage. >>reporter: napa has suffered through 24 serious floods since the civil war. last weekend could easily have been the 25t 25th. outsiders think first of the napa river that floods once every seven years but the creek overruns the banks three times as often. >> our old pair dime was that 4 inches of rain in 6 hours up on western water shed of the napa area would cause a flood on this creek. we are certain now that the capacity of such that number doesn't hold any longer. >>reporter: 12 inches fellas weekend but where bottle neck portion of the creek used to